Cold plasma as an emerging energy-saving pretreatment to enhance food drying: Recent advances, mechanisms involved, and considerations for industrial applications

Background: Cold plasma (CP) is an emerging nonthermal technology that has shown promise in improving food safety. It has been recently used to enhance the drying process as one of the most energy-intensive processes in the food industry. Scope and approach: This review explores the application of CP in food drying. It also discusses the mechanisms involved in the plasma-enhanced drying process. Furthermore, it elaborates on the effects of CP pretreatment on the drying characteristics and quality of dried foods, such as color, texture, and nutritional content. Key findings and conclusion: Most studies (>80%) explored the combination of CP and hot air drying, suggesting a need to research other drying technologies. CP enhances the drying rate and reduces drying energy consumption (similar to 25%), contributing to achieving sustainable development goals (SDGs). It also can improve dried products' quality (e.g., antioxidants and beneficial bioactive content) and reduce 5-hydroxymethylfurfural as a healththreatening chemical. In addition to the generally accepted theory on plasma-induced surface changes, authors hypothesized that possible mechanisms behind the reduced drying time are moisture removal during CP pretreatment and changes in internal structure (within the plasma reactive species penetration depth), which can prevent case-hardening, and consequently shorten the falling rate period of drying. Also, cold plasma treatment can reduce drying time by increasing moisture diffusivity. Industrial applications require further efforts to achieve regulatory bodies' approval and to develop cost-effective upscaled units.